The present invention relates to a method and apparatus for use during the casting of metal and more specifically to a baffle which retards the transfer of heat from a mold structure.
An apparatus which uses inner and outer baffles to retard the transfer of heat from a mold structure to a chill plate during the casting of molten metal in the mold structure is disclosed in U.S. Pat. No. 4,763,716 issued Aug. 16, 1988 and entitled "Apparatus and Method for Use in Casting Articles". The annular outer baffle has a circular inner edge portion which cooperates with an irregular outer side portion of the mold structure to block the transfer of heat from the furnace chamber. Similarly, the inner baffle has a circular outer edge portion which cooperates with an irregular inner side portion of the mold structure to block the transfer of heat. Due to the circular configurations of the baffles and the irregular configurations of the side portions of the mold structure, there will be some space between the edge portions of the baffles and the irregular side portions of the mold structure. This space is to accommodate both the irregular configuration of the side portions of the mold structure and any irregularities which occur during forming of the mold structure.
During a casting operation which calls for directional solidification of molten metal in a mold structure, it is advantageous to have a temperature gradient which is as large as possible across a baffle. The presence of a relatively large temperature gradient across the baffle results in the portion of the mold structure above the baffle being relatively hot and the portion of the mold structure below the baffle being relatively cool. This promotes solidification of the molten metal upwardly from the lower end portion of an article mold cavity. In addition, the establishment of a relatively large temperature gradient between portions of the mold structure disposed above and below the baffle tends to promote the solidification of the molten metal with a fine dendritic structure.
It has been suggested that a baffle could be constructed with a graphite felt layer extending from a pair of support discs toward an irregular side portion of a mold structure. The felt layer is cut to a configuration corresponding to the configuration of a lower end portion of the mold structure. This enables the felt layer to engage the the lower end portion of the mold structure when the mold structure is disposed in a furnace chamber.
As the mold structure is withdrawn from the furnace chamber, the felt layer of this known baffle cannot maintain engagement with the irregular side portion of the mold structure. This results in the opening of space between the felt layer and the mold structure. Of course, heat can be freely transferred through the space between the belt layer and mold structure. This transfer of heat is detrimental to the establishing of a large temperature gradient across the baffle. A baffle having this construction is disclosed in U.S. Pat. No. 3,714,977 issued Feb. 6, 1973 and entitled "Method and Apparatus for the Production of Directionally Solidified Castings."